Curiosity’s pit crew readies the rover for Mount Sharp

Three weeks after landing, Curiosity's engineering team has figured out how to squeeze more surprises and more bandwidth out of the rover while wrapping up a very long list of checkout tasks. A few items remain, but for the most part, the rover is ready to forge a two-year trail up into the foothills of Mt. Sharp.

A voice from the darkness

An interesting thing occurred to the Curiosity engineering team while they were testing what has developed into a Mars orbital communications network. They needed some data to test the system, so why not relay a human voice?

On Monday afternoon, Dave Lavery, the MSL program executive, played back a recording of Charlie Bolden's voice, which became the first human voice transmission from another planet. Relayed up to the Mars Reconnaissance Orbiter via UHF and then to NASA's Deep Space Network via X-band, Bolden's packetized voice made its way through space with remarkable clarity, about 4Mb of data. Not surprisingly, Bolden's message was primarily one of congratulations.

The Curiosity engineering team has found a way to optimize uplink transmissions for higher data volumes than were previously possible.

The distance from Mars to Earth can be up to 400 million kilometers, which can make Curiosity's 15-watt transmitter rather difficult to pick up with the NASA Deep Space Network. Direct transmissions from Curiosity's UHF radio to Earth can achieve only about 1,000bps, at most.

This makes a good argument for taking advantage of the bandwidth available from the three Mars orbiters overhead. The engineering team has been working to closely characterize the transmission network, which consists of three spacecraft—Mars Odyssey, Mars Reconnaissance Orbiter, and the European Space Agency's Mars Express—in an effort to get the highest transmission speeds possible.

Odyssey and MRO orbit about 300-400 kilometers up, with Odyssey passing overhead at about 3am and 3pm, and MRO passing about an hour later at 4am and 4pm. By having Curiosity's radio communicate with the radio on each spacecraft, the transmission rates can be optimized as each one of the relay satellites passes overhead. Data rates have set new records, rising to slightly more than 2Mbps. Curiosity's cumulative data relay volume has reached about 7Gb, about 2-3 times better than Spirit and Opportunity at the same point in their missions.

To infinity and roughly 10 percent beyond

The biggest strain on the data network will be the photos being sent down. To make sure these are the highest quality possible, an engineering team has been working on getting the rover's cameras optimized.

All of Curiosity's cameras, barring MARDI (the downward-looking descent camera), are autofocusing. Before the spacecraft was readied for departure, Curiosity's engineering team attempted to calibrate the rover's cameras correctly for infinity. But, according to Mike Malin, whose company, Malin Space Science Systems, built the rover's cameras, that point turned out to be about 10 percent beyond infinity when the rover got to Mars. The first Mastcam (MAHLI) mosaic sent back was a bit out of focus, so the team has been working to tighten things up.

In the short term, the calibration points are not a problem. The autofocusing mechanisms are mechanical, though, and the team would like them to last as long as possible. Recalibrating the cameras so that they don't need to search for focus at infinity cuts down a huge amount of wear and tear on the focusing mechanisms, and that is what the camera team has been attempting to do this past week. The majority of that work should be complete, and new images are now buffered in the rover.

Unfortunately, there won't be too many more mosaics; those mosaics were done for the engineers, not the science team, and Malin says that the science team is much more likely to want images of specific objects of interest.

Methane! Oops, er, never mind...

The biggest reason for determining the amount of methane in the Martian atmosphere is to determine its origin. After all, on Earth, a lot of methane comes from the presence of life. On Mars, determining the exact amounts and origin of methane in the Martian atmosphere ties into Curiosity's primary mission of determining whether life is present. Recent experiments have reopened the question of whether the Viking landers discovered evidence of microbial life in the Martian soil, making Curiosity's soil and atmospheric tests (and those of the future ExoMars atmospheric probe) even more important. Unfortunately, an experiment that would definitively answer the question is not yet planned.

Also, for the past several years, one of the ideas considered for returning samples (or humans) from Mars has been to send a spacecraft with only enough propellant to land and a store of liquid hydrogen. Once there, the spacecraft would use the Sabatier reaction to create methane and oxygen from the Martian atmosphere, gathering enough propellants to return and gaining a big weight savings over bringing propellants from Earth.

Unfortunately, we don't yet know know the exact composition of the Martian atmosphere. That's why one of the most-anticipated results of the next few months of testing is an accurate measure of Martian atmospheric gases.

Curiosity's Sample Analysis at Mars (SAM) sensor package

When the engineering team began assessing the health of SAM, the Sample Analysis at Mars suite of instruments, some excitement ensued. First, the SAM's turbomolecular pump shut down due to high current draw. When the team looked at the data, the first methane readings were off the charts—equal, in fact, to Earth's methane levels. After the initial excitement died down, the reason became apparent: a little bit of thick Florida atmosphere had come all the way to Mars in the tunable laser spectrometer, causing the pump to hiccup when it tried to evacuate the TLS. SAM's mass spectrometer, not realizing there was a problem, had dutifully reported the methane levels in Florida air. In the end, it made a great impromptu exercise for the team and allowed them to test on Mars against an Earth sample.

Martian methane levels are much, much thinner, in the parts per billion range. Here on Earth, the team is still testing techniques for measuring methane levels on an engineering duplicate of the SAM package. At some point, they'll relay instructions up to SAM to begin collecting and concentrating enough Martian atmosphere for the Tunable Laser Spectrometer (TLS) to accurately measure oxygen, methane, CO2 and other trace gases in the Martian atmosphere. At this point, SAM's Mass Spectrometer and TLS have been assessed, but the gas chromatograph, built in France, remains to be tested.

Road trip!

Today is the first day of Curiosity's Big Adventure. Most of Curiosity's hardware is, at this point, ready for a road trip. It will start with about a 10-meter ride, far enough to demonstrate the long-baseline stereo imaging planned using the MastCams. The rover drivers are ready to get started, and they'll execute a series of drives to put at least 100 meters between the rover and the area affected by the descent stage's landing thrusters. We're finally off to Mt. Sharp!

Not too quickly, though. There's plenty of time for pictures. On Mars, for Curiosity, it's the journey that matters, not the destination.